1. Field of the Invention
The present invention relates to a dynamic route guidance apparatus, and in particular, to a Centrally-Determined Route Guidance System (CDRGS) in which a vehicle transmits data regarding its destination to a control center, and the control center returns to the vehicle information regarding a recommended route to the destination.
2. Description of the Prior Art
Recently, a route guidance system has been suggested in which a vehicle transmits destination data to a road beacon, and a control center connected to the road beacon calculates a recommended route to the destination and notifies the vehicle of the route via the route beacon.
For instance, in a system disclosed in JP Laid-Open Publication No. Hei 7-190794, a vehicle equipped with a device for searching for a route to the destination, compares a recommended route transmitted by a control center and a route found by itself, and selects the most reliable and reasonable route of the two, based on the comparison result.
With this system, since a vehicle transmits unique destination information to a control center, the control center can calculate a route which goes only to a position according to the destination information, such as the nearest link to the destination. The route obtained by the control center sometimes turns out to be incorrect, thus causing the driver to take a longer or alternate route to arrive at the desired destination. The vehicle thus may often have to select a route found by itself, rather than a recommended route. That is, a recommended route based on a consideration of the current traffic conditions may not often be fully utilized in this system.
FIG. 10 schematically shows searching processes carried out by a control center which has received destination data from a vehicle. In the drawing, a thick line represents a link controlled by the control center (a connection line between nodes corresponding to major crossings and points where road beacons are installed; hereinafter referred to as a Universal Traffic Management Systems (UTMS) link); and a thin line represents a shorter link without UTMS link coverage (hereinafter referred to as a non-UTMS link). It is assumed that the nearest link to the destination is not a UTMS link but a non-UTMS link. In order to transmit an UTMS link which is nearest to the destination (the nearest UTMS link) as unique destination data, the vehicle selects and transmits data on Link BC to the control center. Based on this data, the control center calculates a recommended route, i.e., af-fb-bc, and notifies the vehicle of this route. The vehicle then combines the route notified and the route found by itself into a final route, i.e., af-fb-bc-cd-de-eg. However, this route is not the most direct route to the destination, therefore causing the driver to take a detour rather then a shorter, direct path to the desired destination.